Cognitive behavior of rhesus monkeys was assessed in multidisciplinary studies of the neural basis of normal age-related decline. Brain size of old monkeys was found to be equivalent to that of young monkeys. However, myo-inositol, a brain metabolite associated with glial cells, differed significantly between old and young monkeys. Efforts during the next year will continue to emphasize the application of new advances in imaging technology to identify biological markers of advancing age, and to determine which of these markers may correlate with cognitive decline. These studies continue to indicate that the rhesus monkey is an excellent model of age-related cognitive decline in humans, since the monkey displays a pattern of cognitive decline remarkably similar to that seen in our own species.